Решите систему методом введения новых переменных (с решением)

 

1)

х+ху+у=9

х-ху+у=1

2)

ху+х+у=9

х^2у +ху^2=20

 

Помогите, определить в каком  времени стоит, сказуемое

1) One-tenth of all the people who have ever lived on the planet are alive today

2) 97 per cent of population growth is occurring in developing countries.

3) The developing world will have doubled by 2050.

4) The population is becoming economically and demographically polarized.

5)  The population has also got younger.

6)  The girls are staying in school longer in most of the world.

7) Young women who `ve completed secondary school delay their marriage.

8) Statistics like these are frightening.

Происхождение и общее значение слова(термина) полисахарид, дезоксирибоза